As I understand Scripture, humans do not graduate, and become angels when we pass into glory. Angels are different beings, also created, and also assigned a place in the service of God. All service, even our own, is voluntary, and as such, highlights the wonder, beauty and value of God’s love.
“Praise the Lord, you his angels, you mighty ones who do his bidding, who obey his word.” Ps.103 Conversations Within” ts 8/22/